Updated technical manual

[Christian_Bylund]

The technical manual for the Lambda Shield has been updated with important information on how to get the most accuracy and precision out of your device.

The CJ125 controller can be set in calibration mode by transmitting the SPI command (0x569D). This sets the analogue output for oxygen content to its optimal value. The oxygen content output is defined as CJ125_UA and is connected to analogue input 0. This voltage of 1.50V corresponds to a pump current of 0mA and a λ value of 1.00.

Monitoring the 10-bit ADC of the Arduino Uno, 1.50V corresponds to the ADC value of 307. Depending of the voltage powering the CJ125, it affects the accuracy. Either the voltage from the USB- bus or the regulated 5V from the Arduino. See section 3.2 on how to power the Arduino and CJ125 by the supply voltage of the Lambda Shield.

Note, it is normal that the calibration voltage measured by the Arduino ADC does not read the decimal value of 307. The voltage regulator of the Arduino has an accuracy of 1%, which means the voltage powering the CJ125 will also affect its voltage output.

Temperature is also a critical factor in terms of measurement accuracy and precision. The sensors zirconium dioxide membrane operates at a certain temperature, approximately 650°C. The CJ125 controller gives a temperature feedback for heat regulation purposes. The feedback voltage is defined as CJ125_UR and is connected to analogue input 1. In calibration mode, the target temperature (optimal temperature) voltage equivalent will be the output from the CJ125 controller.

Note, a lower voltage indicates a higher temperature. To prevent damage of the sensor when cold and wet, a condensation water phase during heating is necessary and described in full detail by Bosch in the Technical Product Information - Y 258 E00 015e.